Very many chemical reactions, which are of industrial significance, are equilibrium-limited. This means that the reaction between the reaction starting materials to the reaction products does not proceed completely on adjustment of a chemical equilibrium and does not lie completely on the product side. In the chemical equilibrium, therefore, products and starting materials are always present alongside one another. In the case of conventional chemical syntheses, these are, for example, the reactions for the production of methanol from hydrogen and carbon monoxide or carbon dioxide or the production of ammonia from hydrogen and nitrogen, the so-called Haber-Bosch process.
These reactions are carried out industrially nowadays in heterogeneously catalyzed fixed bed or slurry reactors. As described, the starting materials are only partially converted in a single pass through the reactor. Subsequently, the reactant-product mixture is withdrawn and the reaction products are typically separated, wherein the unreacted starting materials are recirculated to a reaction inlet point. The recirculation of partly large amounts of gases on an industrial scale results in high apparatus complexity. Furthermore, still further technical challenges arise, which in their entirety have a distinctly cost-intensive impact on the process.
In practice, there is a loss of pressure in the reactor which has to be compensated for in the case of a significant recirculation. Furthermore, in the case of recirculation, inert and foreign gases accumulate in the circuit, which has a negative influence on the reaction regime and results in a larger reactor volume for example. Furthermore, in the case of recirculation, there is always a loss of starting material which in turn has a negative effect on the conversion efficiency. Furthermore, the amount of gas recycled leads to a high gas volume flow through the reactor which increases the size and thus in turn the costs of the reactor.